Structure–Reactivity Relationships on Supported Metal Model Catalysts: Adsorption and Reaction of Ethene and Hydrogen on Pd/Al2O3/NiAl(110)

Acetylene and Ethylene Hydrogenation on Alumina Supported Pd-Ag Model Catalysts

“…It is clear that ethane production is strongly enhanced in the presenc e of sub-surface hydrogen. This behavior is essentially identical to that previously observed for ethylene in our work and in the literature [21,24]. Stacchiola and Tysoe found that the presence of sub-surface hydrogen increased the amount of p-bonded ethylene on the surface of Pd(111) [24].…”

“…Basically, acetylene is dehydrogenated on Pd giving rise to a hydrogen multi-peak desorption signal extending up to 500 K, i.e. similar to that observed for ethylene [21]. No ethane, but traces of ethylene were detected, desorbing at 250-300 K. These species can be assigned either to the self-hydrogenation reaction (as observed on Pd(111) [13]) or reaction with hydrogen from the vacuum background.…”

“…The desorption temperatures of ethane formed from acetylene ( Fig. 2b) and ethylene [21] on the particles also show strong similarities (around 200 K). These results suggest that, under the conditions studied, full hydrogenation to alkane is always favored by sub-surface hydrogen independently of the nature of hydrocarbon precursor, alkyne or alkene.…”

“…We have previously shown that the production of ethane from ethylene critically depends on the amounts of hydrogen residing in the sub-surface region of Pd particles [17,21]. In order to study this effect for hyd rogenation of acetylene, we adsorbed hydrogen on pure Pd particles at different temperatures (200 -300 K) followed by adsorption of acetylene at 100 K. Fig.…”

“…When the sample is exposed to H 2 at 300 K, a single "high temperature" (HT) state at ~ 330 K is observed in the TPD spectra, which exhibits second-order kinetics on H 2 exposure [21] and has been assigned to the surface H species recombining and desorbing upon heating, similar to H 2 on Pd(111). However, when the Pd particles are exposed below 200 K to the same amounts of H 2 , desorption emerges at much lower temperatures than on Pd(111) [17].…”